'Atomic' clocks go dark in Japan

People living in earthquake-, tsunami- and now nuclear radiation-ravaged Fukushima have it bad enough. So when those with high-spec digital "atomic watches" saw their timepieces were failing, some thought radiation from the stricken Daiichi plant was interfering with the watches' workings.

They needn't have worried. The watches were not affected by radiation as feared - they don't run on anything like atomic power themselves. Instead, the radio signal they rely on a radio transmission from a true atomic clock - which measures the oscillations of non-radioactive caesium atoms - to keep precise time.

It was the radio signal from a transmission station at mount Otakadoya that had gone dark. The station is located 16 kilometres from the Daiichi power station, within the 20 km zone of exclusion imposed when the plant started leaking radiation. It typically broadcasts its signal as one of two Selected Standard Frequency and Time Signal Stations in Japan.

The other lies in the south of Japan in Kyushu but broadcasts on a different frequency, leaving those devices relying on Fukushima's atomic clock time transmitter without an automatic update and their "atomic watches" out of kilter.

According to the National Institute of Information and Communications and Technology, which usually transmits the 40 kilohertz signal, broadcasts ceased a day after the massive Tohoku earthquake struck the region on 11 March. Officials at the institute said they have no idea when service might resume.